1. Field of the invention
The present invention relates to a poly-V grooved pulley of light-weight sheet metal for use with a poly-V belt in drive systems, and more particularly to an improved method for manufacturing a poly-V grooved pulley having a hub wall and a cylindrical poly-V grooved flange wall integral with the hub wall.
2. Description of the Prior Art
As is pointed out in the specification of U.S. Pat. No. 3,977,264 of Sproul, prior poly-V grooved pulleys, such as shown in U.S. Pat. No. 3,368,376 of Previte, have had groove-forming walls which are thinner than the parent metal in the pulley flange in which the grooves are formed; which are non-uniform in thickness because of a different inner and outer angular contour of the V-groove formations; and which inherently involve stretching the metal in the V-groove walls. This results in insufficient strength and rigidity of the pulley, causing undesirable cracks in the pulley during operation under heavy loading.
To overcome such drawbacks as described above, it has been proposed to provide a sheet metal poly-V pulley structure having roller spun cold-worked thickened groove-forming walls provided with a plurality of relatively narrow deep V-grooves formed in an axially extending pulley flange wall, as has been disclosed in U.S. Pat. No. 3,977,264 of Sproul. During the manufacturing processes of the poly-V grooved pulley of Sproul, rounded V-shaped groove walls forming the valleys and crests in the stage blank are axially squeezed and compressed to each other to form a sinuous-shaped flange wall in which the metal is roller worked, compressed, displaced and extruded in various zones to form the V-shaped pulley grooves. In such manufacturing processes, buckling portions inevitably occur between the inner rounded surfaces of the thickened valley walls, which result in undesirable cracks in the V-grooved flange wall during operation under heavy loading.
For the purpose of overcoming similar problems in the prior art, it has been proposed to thicken the appropriately cylindrical flange wall portion of a pulley blank without thickening the hub portion of pulley blank so that the flange wall portion will be thicker than the thickness of the parent metal used to form the pulley blank, as has been described in U.S. Pat. No. 4,273,547 of Bytzek. During the process of thickening the parent metal, the flange wall portion is partially collapsed in an axial direction, and the exterior periphery of the partially collapsed section is rolled while the interior periphery of the same is supported in a straight axially extending configuration thereby to form the V-shaped pulley grooves in the thickened flange wall portion. In such formation of the thickened poly-V grooved pulley flange, it is, however, difficult to uniformly collapse the cylindrical flange wall portion without buckling in its metal, and it is further difficult to precisely form the V-shaped pulley grooves by rolling in the thickened flange wall without any interengaged portions. The difficulties will increase if the collapsing process is adapted to thicken the flange wall portion in a wider area. For this reason, it is apparent that if the flange wall portion is collapsed in an irregular manner, there will occur undesirable buckling in the thickened flange wall, resulting in cracks in the poly-V grooved pulley during operation under heavy loading.